There are quite a number of situations in which a graded surface must be precisely horizontal. A motor grader blade has a variety of adjustments which permit it to be oriented with the cutting edge of its blade precisely horizontal; but power earth movers such as elevating scrapers have no such capability. Nevertheless, there are numerous circumstances under which final grading could be handled with a power earth mover provided it could be assured that the cutting edge of the earth mover bowl is exactly horizontal.
The mechanics and geometry of earth mover bowl mounting are such that normal manufacturing tolerances make it very unlikely that the cutting edge of a bowl will be horizontal. The bowl is carried upon arms which are pivoted at opposite sides of the vehicle. Manufacturing problems make it impossible to get the arm pivot centers precisely coaxial while also getting the arms identically mounted on the pivots and the two sides of the scraper bowl identically mounted upon the arms. These have created insurmountable problems for making a power earth mover which can be used to make horizontal finishing cuts on a grading operation.